1. Field of Invention
The present invention relates to a micro-electro-mechanical system (MEMS) device with enhanced structural strength, especially a MEMS device having a top metal layer with a plurality of metal segments and/or a lowest metal layer including a continuous structure.
2. Description of Related Art
FIG. 1 shows a prior art MEMS device 10, which for example can be used for a stator or a rotor. The MEMS device 10 includes a micro-electro-mechanical structure 101 and a signal transmission structure 102, wherein an operation of the MEMS structure 101 generates an electric signal and the electric signal is transmitted through the signal transmission structure 102. When the MEMS device 10 is a stator, the MEMS structure 101 for example can be connected to a substrate Sub through a fixing member 103. When the MEMS device 10 is a rotor, the MEMS structure 101 for example can be connected to the substrate Sub through a flexible member (shown schematically as a spring for example). The MEMS device 10 can be manufactured by a CMOS semiconductor manufacturing process, in which plural metal layers M1-Mt and plural dielectric layers are deposited and patterned on the substrate Sub, and plural via plugs are formed in the dielectric layers to connect the metal layers so as to form a designed structure.
The prior art MEMS device 10 has the following structure features:
1. The top metal layer Mt has a continuous structure.
2. The signal transmission structure 102 is formed by a portion M1S of the first metal layer M1; therefore, in order to prevent the signal transmitted through the signal transmission structure 102 from being affected by a nearby electric field and also avoid stiction which may occur in the manufacturing process and in the operation of the MEMS device, the second metal layer M2 has a disconnection area above the portion M1S to leave a buffer space. However, this recess weakens the strength of the MEMS structure 101.
When the strength of the MEMS structure 101 is not enough, it is liable to warp or distort. For example, when the environment temperature increases, the MEMS device 10 can easily deform to affect the performance of the MEMS device 10.
FIG. 6A shows deformation of the MEMS device 10 as the temperature increases. In the figure, the horizontal axis represents distance in the direction X of FIG. 1, and the vertical axis represents deformation, wherein the temperature T2 is higher than the temperature T1. As shown in the figure, the deformation at temperature T2 is higher than the deformation at temperature T1, and the deformation increases alone the direction X to an extent that can affect the stability of the structure and the function of the device in operation.
In view of the aforementioned deficiencies of the prior art, the present invention provides a MEMS device with enhanced structure strength whereby there is little or no deformation caused by temperature change or other reasons, to avoid stiction, maintain the structure stability, and improve the signal transmission performance.